The present invention relates to a method of and a device for regulating rotary speeds of an internal combustion engine of a motor vehicle having an idling speed regulator or idling speed volume efficiency regulator for producing a control signal maintaining a minimum rotary speed, and a push or overrun cutoff device producing a cutoff signal for interrupting fuel supply when rotary speed of the engine exceeds the idling speed and simultaneously the motor vehicle is in an overrun or pushing operational condition.
Devices for regulating rotary speed of internal combustion engines are known from prior art. For example, it is conventional to provide an idling fuel mixture charge regulator which can operate in an air bypass arranged parallel to the throttle while usually a two winding rotary adjustor. Such prior art idling volumetric efficiency regulators (designed either by an analog or digital technology), by considering the momentary actual rotary speed of the engine, or the desired rotary speed and other peripheral data, are in position to maintain proper idling operation of the internal combustion engine, for example in the pulling or pushing (coasting) operation of the vehicle and during transition from the pushing operation into the idling one.
It has been known in internal combustion engines to interrupt during operation the fuel supply in the case when at higher or high rotary speeds the throttle plate is closed, that means when the engine is in the so-called overrun or pushing operational condition. Such a pushing operational condition occurs also in the case when the engine runs at a higher speed than that corresponding in the case of gasoline engine to the position of throttle plate or in the case of a diesel engine to the quantity of injected fuel. If the internal combustion engine is in an overrun or pushing operational condition then an increase of working power is undesired and consequently, the quantity of fuel supplied to the engine by the corresponding fuel mixture supply device (carburator, fuel injection system and the like) is either reduced or completely set to zero (overrun or push cutoff).
However, such prior art regulators do not guarantee a problem free operation when the two systems, which of necessity operate independently from one another, are brought into action. Such problems may result for example, when due to a corresponding activation of the idling volumetric efficiency regulator, the idling air filling adjuster is wide open due to operative conditions taken into consideration (for example during start or due to excessive warming up) and simultaneously the actual rotary speed of the engine momentarily exceeds the rotary speed which has been preset for the overrun or push cutoff. In the latter case both systems act: the overrun or push cutoff function is activated so that for example under certain extreme conditions a so-called sawtooth behavior (uncontrollable oscillating behavior) may occur. Under extreme conditions when the engine is cold, the engine may even become dead.